Under barbiturate anesthesia, microelectrode recordings from the trigeminal ganglion of monkey are performed and electrical activity is recorded and stored on magnetic tape. Thermal and noxious heat stimuli are delivered with a precisely-controlled thermode which has a temperature range of 20 degrees C to 60 degrees C and can produce a temperature change of 10 degrees C at the thermode-skin junction within one second. Data is analyzed with the aid of an on-line, real-time computer system.